Passenger automobiles typically have one or more passenger entryways defined by a door sill attached to the exterior body frame of the vehicle. The vehicle door sill provides an entryway transition between the exterior of the vehicle and an interior compartment, for example, a passenger compartment. The door sill is generally configured to interface with a door connected by a hinge to the body frame at a forward position, for example, at an A-pillar of a unibody chassis. When closed, the door generally interfaces with a latching mechanism located at a rearward position, for example, at a B-pillar of a unibody chassis. The door sill provides a good seal between the door and the body frame of the vehicle, thereby reducing vibration and noise within the passenger compartment.
Door sills are commonly made from inexpensive lightweight materials such as plastics, and may be readily damaged in a collision, particularly a side impact collision. Side impact protection for a passenger seated in the passenger compartment of a vehicle is thus provided, if at all, by the vehicle frame and doors. It is known to improve passenger side impact protection by incorporating reinforcements, for example steel beams, within the doors of the vehicle. However, this adds to the cost and weight of the door and the vehicle, and can make it more difficult for a passenger to open or close the door.
It is also known to install passive side air bag assemblies to protect a passenger during a side impact with an object such as another vehicle. However, airbags also add to the cost and complexity of the vehicle, and the air bag assemblies may not provide complete passenger protection during a side impact with a massive object such as a heavy truck or concrete structure. The side air bag deployment system, which is usually built into the passenger seat or ceiling, may also negatively affect the aesthetic appearance of the vehicle interior. Airbags also do not protect the vehicle frame from damage in a side impact collision, leading to expensive repairs to the vehicle after such a collision, particularly for vehicles manufactured with a unibody frame construction.